The Cascading Curtain
This is a relic of the days when "the boys" (Abraxas and his brothers) were all looking for their 'personal space'. It was carved out and modified by Misrada, only about 300 yards from the main building. The water in the waterfall will strip flesh from any non-Rookou (or someone within three meters of a Rookou as their "guest"), and cause painful boils even to Rookous if they fail to recite the family motto as they pass through. The magic holds equally for house elves. So far, Draco's best efforts have been unable to remove the horror from the water, although it is seemingly diluted, as a Muggle teenager got into the cave with only a few first-degree burns. He was patched up, Obliviated and given a memory than left him with a total antipathy for the idea of setting foot on the grounds again.
The caverns beyond are enormous, and divided into twelve largely separate sections, eleven of which are roughly "room" sized. Currently it has little lighting, but that can be readily remedied with magic.
Since Misrada was the most gleefully sadistic member of a family that prided itself on the artistry of its torture, there could be any number or type of 'souvenirs' in here. There are certainly elements from earlier eons only half-unearthed.
Adera Rookou is the current occupant. She is slowly making the place truly her own.
The introductory section of the complex.
The "meet and greet" segment of the sequence.
The research and storage zone.
Referred to by the one Muggle visitor who ever came in as "Devon" and "3D", this table-filled area offers options for eating and talking in comfort, or just reading in a relaxed environment.
The sleeping quarters.
This is Adera's bedroom and lounge area, on the far side of Cavern Four.
This seemingly unending space would have the potential to provide a refuge for all occupants of the 4,800 acres.